U.S. patent application number 13/710608 was filed with the patent office on 2013-06-13 for transparent conductive material, dispersion liquid, transparent conductive film, and methods for manufacturing same.
The applicant listed for this patent is Hideaki Hirabayashi, Masao Kon, Hirotoshi MURAYAMA, Tsuyoshi Noma, Masashi Yamage. Invention is credited to Hideaki Hirabayashi, Masao Kon, Hirotoshi MURAYAMA, Tsuyoshi Noma, Masashi Yamage.
Application Number | 20130147089 13/710608 |
Document ID | / |
Family ID | 48571261 |
Filed Date | 2013-06-13 |
United States Patent
Application |
20130147089 |
Kind Code |
A1 |
MURAYAMA; Hirotoshi ; et
al. |
June 13, 2013 |
TRANSPARENT CONDUCTIVE MATERIAL, DISPERSION LIQUID, TRANSPARENT
CONDUCTIVE FILM, AND METHODS FOR MANUFACTURING SAME
Abstract
According to one embodiment, a transparent conductive material
is used for a transparent conductive film. The transparent
conductive material includes nanographene having a polar group at a
surface of the nanographene.
Inventors: |
MURAYAMA; Hirotoshi;
(Kanagawa-ken, JP) ; Hirabayashi; Hideaki;
(Kanagawa-ken, JP) ; Yamage; Masashi;
(Kanagawa-ken, JP) ; Noma; Tsuyoshi;
(Kanagawa-ken, JP) ; Kon; Masao; (Kanagawa-ken,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MURAYAMA; Hirotoshi
Hirabayashi; Hideaki
Yamage; Masashi
Noma; Tsuyoshi
Kon; Masao |
Kanagawa-ken
Kanagawa-ken
Kanagawa-ken
Kanagawa-ken
Kanagawa-ken |
|
JP
JP
JP
JP
JP |
|
|
Family ID: |
48571261 |
Appl. No.: |
13/710608 |
Filed: |
December 11, 2012 |
Current U.S.
Class: |
264/293 ;
252/500; 558/412; 977/734; 977/896 |
Current CPC
Class: |
Y10S 977/734 20130101;
Y10S 977/896 20130101; B82Y 30/00 20130101; H01B 1/04 20130101;
H01B 1/12 20130101 |
Class at
Publication: |
264/293 ;
252/500; 558/412; 977/734; 977/896 |
International
Class: |
H01B 1/12 20060101
H01B001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2011 |
JP |
2011-271400 |
Claims
1. A transparent conductive material used for a transparent
conductive film and comprising nanographene having a polar group at
a surface of the nanographene.
2. The transparent conductive material according to claim 1,
wherein the polar group is at least one selected from the group
consisting of a hydroxy group, a methyl group, an aldehyde group, a
carboxyl group, a nitro group, an amino group, a hydroxyl group, a
mercapto group, an organic amino group, an alkoxy group, a cyano
group, a nitromethyl group, and a bis(alkoxycarbonyl)methyl
group.
3. The transparent conductive material according to claim 1,
further including a nonionic water-soluble resin with a visible
light transmittance of 80% or more.
4. The transparent conductive material according to claim 1,
further including poly(ethylene oxide).
5. A dispersion liquid comprising: a solvent; and a transparent
conductive material used for a transparent conductive film and
including nanographene having a polar group at a surface of the
nanographene.
6. The dispersion liquid according to claim 5, further including a
nonionic water-soluble resin with a visible light transmittance of
80% or more.
7. A transparent conductive film comprising a transparent
conductive material used for a transparent conductive film and
including nanographene having a polar group at a surface of the
nanographene.
8. The transparent conductive film according to claim 7, wherein
the polar group is at least one selected from the group consisting
of a hydroxy group, a methyl group, an aldehyde group, a carboxyl
group, a nitro group, an amino group, a hydroxyl group, a mercapto
group, an organic amino group, an alkoxy group, a cyano group, a
nitromethyl group, and a bis(alkoxycarbonyl)methyl group.
9. The transparent conductive film according to claim 7, further
including a nonionic water-soluble resin with a visible light
transmittance of 80% or more.
10. The transparent conductive film according to claim 7, further
including poly(ethylene oxide).
11. A method for manufacturing a dispersion liquid comprising:
supplying hydrocarbon into a reducing atmosphere provided with a
heated catalyst and producing a carbon nanotube on the catalyst;
treating the carbon nanotube by oxidation to produce nanographene
and introduce a first polar group onto a surface of the
nanographene; and producing a dispersion liquid by neutralizing a
liquid after production of nanographene by the oxidation
treatment.
12. The method according to claim 11, wherein the oxidation
treatment is performed using at least sulfuric acid.
13. The method according to claim 11, wherein the neutralization is
performed using an anion exchange resin.
14. The method according to claim 11, further comprising
substituting the first polar group with a second polar group using
a nucleophile.
15. The method according to claim 11, further comprising adding a
nonionic water-soluble resin with a visible light transmittance of
80% or more.
16. A method for manufacturing a transparent conductive material
comprising: manufacturing a dispersion liquid using a method for
manufacturing a dispersion liquid including: supplying hydrocarbon
into a reducing atmosphere provided with a heated catalyst and
producing a carbon nanotube on the catalyst; treating the carbon
nanotube by oxidation to produce nanographene and introduce a first
polar group onto a surface of the nanographene; and producing a
dispersion liquid by neutralizing a liquid after production of
nanographene by the oxidation treatment; and drying the dispersion
liquid.
17. The method according to claim 16, further comprising
substituting the first polar group with a second polar group using
a nucleophile.
18. The method according to claim 16, further comprising adding a
nonionic water-soluble resin with a visible light transmittance of
80% or more.
19. A method for manufacturing a transparent conductive film
comprising: manufacturing a dispersion liquid using a method for
manufacturing a dispersion liquid including: supplying hydrocarbon
into a reducing atmosphere provided with a heated catalyst and
producing a carbon nanotube on the catalyst; treating the carbon
nanotube by oxidation to produce nanographene and introduce a first
polar group onto a surface of the nanographene; and producing a
dispersion liquid by neutralizing a liquid after production of
nanographene by the oxidation treatment; applying the dispersion
liquid to a region for forming a transparent conductive film; and
drying the applied dispersion liquid.
20. The method according to claim 19, further comprising using a
nanoimprint method to form a transparent conductive film having a
desired configuration before the applied dispersion liquid becomes
completely dry.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2011-271400, filed on Dec. 12, 2011; the entire contents of which
are incorporated herein by reference.
FIELD
[0002] Embodiments described herein relate generally to a
transparent conductive, a dispersion liquid, a transparent
conductive film, and methods for manufacturing the same.
BACKGROUND
[0003] A transparent conductive film is used in electronic devices
such as flat panel displays, solar cells, and touch panels.
[0004] Some of such transparent conductive films include
nanocarbon, such as carbon nanotubes, as a transparent conductive
material. By using a material including nanocarbon as a transparent
conductive material, a transparent conductive film having high
transparency and conductivity can be obtained.
[0005] However, these days further improvement in the transparency
and conductivity of the transparent conductive film is desired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a graph for illustrating the transparency of
transparent conductive films;
[0007] FIGS. 2A and 2B are schematic diagrams for illustrating the
conductivity of transparent conductive films;
[0008] FIG. 3 is a flow chart for illustrating a method for
manufacturing a transparent conductive material, a method for
manufacturing a dispersion liquid, and a method for manufacturing a
transparent conductive film according to the embodiment; and
[0009] FIG. 4 is a graph for illustrating the production of
nanographene by oxidation treatment.
DETAILED DESCRIPTION
[0010] In general, according to one embodiment, a transparent
conductive material is used for a transparent conductive film. The
transparent conductive material includes nanographene having a
polar group at a surface of the nanographene.
[0011] Various embodiments will be illustrated hereinafter with
reference to the accompanying drawings.
[0012] For transparent conductive films used in electronic devices
etc., those including nanocarbon such as carbon nanotubes are
known. For example, by using a transparent conductive film
including carbon nanotubes, a transparent conductive film with low
electric resistance can be obtained. Since the diameter dimension
of the molecular chain of the carbon nanotube is a nanometer level,
a transparent conductive film with high transparency can be
obtained.
[0013] However, these days further improvement in the transparency
and conductivity of the transparent conductive film is desired.
[0014] The inventors' investigation shows that, by using a
transparent conductive film including nanographene, conductivity
and transparency can be improved as compared to transparent
conductive films including carbon nanotubes.
[0015] Here, when a transparent conductive film including
nanocarbon such as carbon nanotubes is manufactured, a dispersion
liquid in which nanocarbon is dispersed in a medium such as water
is produced, the produced dispersion liquid is applied, and the
applied dispersion liquid is dried to form the transparent
conductive film.
[0016] However, if nanographene is simply dispersed in a medium
such as water, pieces of nanographene may aggregate to cause an
in-plane distribution in the characteristics of the transparent
conductive film formed. For example, transparency and conductivity
may greatly vary with the in-plane position in the transparent
conductive film.
[0017] Hence, when nanographene is dispersed in a medium such as
water, it is necessary to improve dispersion quality.
[0018] In view of this, a transparent conductive material according
to the embodiment is configured to include nanographene having a
polar group at its surface. By using nanographene having a polar
group at its surface, dispersion quality can be improved when the
nanographene is dispersed in a medium such as water.
[0019] In this case, the polar group may be a functional group
directly introduced onto the surface of nanographene (corresponding
to an example of a first polar group). As such a polar group, for
example, a hydroxy group, a methyl group, an aldehyde group, a
carboxyl group, a nitro group, and the like directly introduced
onto the surface of nanographene by performing oxidation treatment
or the like may be illustrated.
[0020] As the oxidation treatment, for example, a treatment using
sulfuric acid and a catalyst such as potassium permanganate, a
treatment with a mixed acid solution in which sulfuric acid and
nitric acid are mixed, and the like may be illustrated. For
example, the oxidation treatment may be performed using at least
sulfuric acid.
[0021] The polar group may be also a group obtained by directly
introducing a functional group onto the surface of nanographene and
substituting the functional group using a nucleophile
(corresponding to an example of a second polar group). As such a
polar group, for example, an amino group, a hydroxyl group, a
mercapto group, an organic amino group, an alkoxy group, a cyano
group, a nitromethyl group, a bis(alkoxycarbonyl)methyl group, and
the like introduced by performing oxidation treatment or the like
to introduce a nitro group directly onto the surface of
nanographene and substituting the nitro group may be
illustrated.
[0022] As the substitution using a nucleophile, the case may be
illustrated where a nitro group introduced by performing oxidation
treatment or the like is reduced using tin (Sn), which is a
nucleophile, and concentrated hydrochloric acid and is substituted
with an amino group or the like.
[0023] The dispersion quality of nanographene having a polar group
may be degraded depending on the type of the medium included in the
dispersion liquid, the type of a resin described later, etc. In
such a case, if it is possible to change the polar group by
substitution, an appropriate polar group can be selected in
accordance with the type of the medium, the type of the resin, etc.
Consequently, the degradation in dispersion quality due to the type
of the medium, the type of the resin, etc. can be suppressed.
[0024] In the transparent conductive material according to the
embodiment, a resin may be further put in as a binder for improving
the strength etc. of the transparent conductive film. As the resin
put into the dispersion liquid, for example, a water-soluble resin
and the like may be illustrated. In this case, to ensure the
transparency of the transparent conductive film, a water-soluble
resin with a visible light transmittance of 80% or more may be
used. A nonionic water-soluble resin may be used in order to
prevent the polar group introduced into nanographene from changing.
As the nonionic water-soluble resin with a visible light
transmittance of 80% or more, for example, poly(ethylene oxide) and
the like may be illustrated.
[0025] A dispersion liquid according to the embodiment may include
a transparent conductive material according to the embodiment and a
medium. In the medium included in the dispersion liquid, water
included in the sulfuric acid solution and/or the nitric acid
solution used for oxidation treatment, water produced by
neutralization using an anion exchange resin, water added during
dilution, etc. are included.
[0026] A transparent conductive film according to the embodiment
may include a transparent conductive material according to the
embodiment. For example, it may be a transparent conductive film in
which at least one of nanographene having a polar group and an
aggregate of nanographene having a polar group is dispersed. It may
be also one further including a water-soluble resin such as
poly(ethylene oxide). Such a transparent conductive film can be
formed by, for example, applying a dispersion liquid according to
the embodiment to the region where the transparent conductive film
will be formed and drying the applied dispersion liquid.
[0027] Next, the transparency and conductivity of the transparent
conductive film according to the embodiment are illustrated.
[0028] FIG. 1 is a graph for illustrating the transparency of
transparent conductive films.
[0029] "90" in FIG. 1 is the case of a transparent conductive film
including 5 wt % carbon nanotubes (a transparent conductive film
according to a comparative example). "100" in FIG. 1 illustrates an
example of the transparent conductive film according to the
embodiment, and is the case of a transparent conductive film
including 5 wt % nanographene having a polar group. In "90" and
"100", the other components of the transparent conductive films are
mainly poly(ethylene oxide).
[0030] "90" in FIG. 1 shows the measurement results for a
transparent conductive film produced by a method in which a
dispersion liquid including carbon nanotubes and poly(ethylene
oxide) is applied onto a glass substrate and the applied dispersion
liquid is dried.
[0031] "100" in FIG. 1 shows the measurement results for a
transparent conductive film produced in an example described
later.
[0032] The transparency of the transparent conductive films was
evaluated using the transmittance of visible light. The
transmittance of visible light was measured using the
spectrophotometer UV-3100 (the multipurpose large-size sample
chamber MPC-3100 installation type) manufactured by Shimadzu
Corporation.
[0033] As shown in FIG. 1, in the case of the transparent
conductive film according to the embodiment, the transmittance of
visible light can be made higher than in the case of the
transparent conductive film including carbon nanotubes.
[0034] That is, the transparent conductive film according to the
embodiment can improve transparency as compared to the transparent
conductive film including carbon nanotubes.
[0035] FIGS. 2A and 2B are schematic diagrams for illustrating the
conductivity of transparent conductive films.
[0036] FIG. 2A is a schematic diagram showing the distribution of
the surface electric resistance value of a transparent conductive
film including 5 wt % carbon nanotubes (a transparent conductive
film according to the comparative example). FIG. 2B illustrates an
example of the transparent conductive film according to the
embodiment, and is a schematic diagram showing the distribution of
the surface electric resistance value of a transparent conductive
film including 5 wt % nanographene having a polar group.
[0037] In FIGS. 2A and 2B, the other components of the transparent
conductive films are mainly poly(ethylene oxide).
[0038] FIG. 2A shows the measurement results for a transparent
conductive film produced by a method in which a dispersion liquid
including carbon nanotubes and poly(ethylene oxide) is applied onto
a glass substrate and the applied dispersion liquid is dried.
[0039] FIG. 2B shows the measurement results for a transparent
conductive film produced in the example described later.
[0040] The conductivity of the transparent conductive films was
evaluated using the surface electric resistance value of the
transparent conductive films. The surface electric resistance value
of the transparent conductive films was measured using the Hiresta
UP MCP-HT450 type manufactured by Mitsubishi Chemical Analytech
Co., Ltd.
[0041] As shown in FIGS. 2A and 2B, in the case of the transparent
conductive film according to the embodiment, the surface electric
resistance value can be made lower than in the case of the
transparent conductive film including carbon nanotubes. In this
case, the average value of the surface electric resistance value of
the transparent conductive film including 5 wt % carbon nanotubes
was 2.33.times.10.sup.10.OMEGA., and the average value of the
surface electric resistance value of the transparent conductive
film according to the embodiment was
5.25.times.10.sup.8.OMEGA..
[0042] Next, a method for manufacturing a transparent conductive
material, a method for manufacturing a dispersion liquid, and a
method for manufacturing a transparent conductive film according to
the embodiment are illustrated.
[0043] FIG. 3 is a flow chart for illustrating a method for
manufacturing a transparent conductive material, a method for
manufacturing a dispersion liquid, and a method for manufacturing a
transparent conductive film according to the embodiment.
[0044] Here, nanographene is generally produced from graphite.
However, producing nanographene from graphite causes complicated
production processes, increased costs, etc.
[0045] Hence, in the method for manufacturing a transparent
conductive material according to the embodiment, carbon nanotubes
are produced and nanographene is produced from the produced carbon
nanotubes.
[0046] First, carbon nanotunes serving as the source material in
producing nanographene are produced (step S1).
[0047] Examples of the method for producing carbon nanotubes
include the arc discharge method, the laser deposition method, the
chemical vapor deposition (CVD) method, etc.
[0048] Thus, these production methods may be used to produce carbon
nanotubes. However, it is difficult for these production methods to
produce carbon nanotubes in a large amount. The arc discharge
method and the laser deposition method can produce carbon nanotubes
of good crystallinity, whereas it may be difficult for chemical
vapor deposition to produce carbon nanotubes of good
crystallinity.
[0049] In view of this, in the method for manufacturing a
transparent conductive material according to the embodiment, the
method illustrated below is used to produce carbon nanotubes.
[0050] In the production of carbon nanotubes, first, hydrocarbon is
supplied into a reducing atmosphere (into an atmosphere filled with
a reducing gas) in which a heated catalyst is provided and carbon
nanotubes are produced on the catalyst.
[0051] The catalyst may be a flat plate made of a metal, for
example. The metal may be, for example, one including iron such as
carbon steel and stainless steel. By removing an oxide film formed
on the surface of the catalyst, the activity as a catalyst can be
improved.
[0052] Using a flat plate facilitates the scraping off of carbon
nanotubes described later.
[0053] The temperature of the catalyst may be, for example, not
less than 600.degree. C. and not more than 750.degree. C.
[0054] The hydrocarbon may be, for example, ethanol, ethylene,
propane, methane, carbon monoxide, benzene, or the like.
[0055] It is also possible to supply hydrocarbon heated beforehand
at approximately 350.degree. C. into a reducing atmosphere.
[0056] The hydrocarbon supplied into the reducing atmosphere is
pyrolyzed. By the hydrocarbon being pyrolyzed, carbon atoms adhere
onto the catalyst. When carbon atoms attached onto the catalyst
have reached the saturation state, carbon grows in a crystal form
to produce carbon nanotubes.
[0057] Next, the carbon nanotubes produced on the catalyst are
scraped off mechanically.
[0058] By repeating the production and scraping off of carbon
nanotubes, carbon nanotubes of good crystallinity can be easily
produced in a large amount.
[0059] Next, the carbon nanotubes are treated by oxidation, and
thus nanographene is produced and polar groups are introduced onto
the surface of the nanographene (step S2).
[0060] By treating the carbon nanotubes by oxidation, the carbon
nanotubes are broken up to produce nanographene. In addition, by
performing oxidation treatment, polar groups are introduced onto
the surface of the nanographene.
[0061] As the oxidation treatment, for example, a treatment using
sulfuric acid and a catalyst such as potassium permanganate, a
treatment using a mixed acid solution in which sulfuric acid and
nitric acid are mixed, and the like may be illustrated.
[0062] In the case where a mixed acid solution in which sulfuric
acid and nitric acid are mixed is used for the oxidation treatment,
the concentration of nitric acid may be set to 10 wt % or more. If
the concentration of nitric acid is less than 10 wt %, the
efficiency of introducing polar groups may be reduced.
[0063] FIG. 4 is a graph for illustrating the production of
nanographene by oxidation treatment.
[0064] "110" in FIG. 4 shows the particle size distribution in a
liquid before carbon nanotubes are treated by oxidation, and "120"
shows the particle size distribution in a liquid after carbon
nanotubes are treated by oxidation.
[0065] FIG. 4 shows the measurement results of the particle size
distribution in a liquid produced in the example described later.
The particle size distribution in the liquids was measured using
the zeta potential and particle size distribution measurement
apparatus ELSZ-2 manufactured by Otsuka Electronics Co., Ltd.
[0066] As shown in FIG. 4, by treating carbon nanotubes by
oxidation, nanographene of less than 100 nm can be produced.
[0067] The length of nanographene in this case is the maximum
length in the tree-dimensional dimensions (e.g. the cross-sectional
dimensions and length). For example, when the length is at a
maximum out of the dimensions of the portions of nanographene,
nanographene with a length of less than 100 nm can be produced.
[0068] A nucleophile may be used to substitute the polar group
introduced by oxidation treatment with another polar group, as
necessary (step S3).
[0069] For example, a nitro group introduced by oxidation treatment
is substituted with an amino group, a hydroxyl group, a mercapto
group, an organic amino group, an alkoxy group, a cyano group, a
nitromethyl group, a bis(alkoxycarbonyl)methyl group, or the
like.
[0070] As the substitution using a nucleophile, for example, the
case may be illustrated where a nitro group is reduced using tin
(Sn), which is a nucleophile, and concentrated hydrochloric acid
and is substituted with an amino group or the like.
[0071] Next, the liquid after nanographene is produced by oxidation
treatment is neutralized to produce a dispersion liquid (step
S4).
[0072] The liquid after nanographene is produced by oxidation
treatment has become acid. This liquid may be used as a dispersion
liquid, but it may cause corrosion etc. depending on the object to
which the dispersion liquid is applied. Hence, it is preferable to
neutralize the liquid after nanographene is produced by oxidation
treatment and make the liquid neutral.
[0073] Here, the neutralization can be performed by adding an
alkaline agent. However, if an alkaline agent is added, the polar
group introduced onto the surface of nanographene may change.
[0074] In view of this, in the embodiment, the neutralization is
performed by putting an anion exchange resin (a basic resin) into
the liquid after nanographene is produced by oxidation
treatment.
[0075] In this case, filtration etc. is performed after the
neutralization to remove the anion exchange resin.
[0076] To protect the anion exchange resin, water or the like may
be added for dilution.
[0077] Next, a water-soluble resin etc. may be added to the
dispersion liquid as necessary (step S5).
[0078] For example, a water-soluble resin with a visible light
transmittance of 80% or more may be added. The water-soluble resin
added may be a nonionic water-soluble resin in order to prevent the
polar group introduced into nanographene from changing. As the
nonionic water-soluble resin with a visible light transmittance of
80% or more, for example, poly(ethylene oxide) and the like may be
illustrated.
[0079] Thus, a medium and nanographene having a polar group at its
surface are included in the dispersion liquid. A water-soluble
resin such as poly(ethylene oxide) may be further included.
[0080] In the medium included in the dispersion liquid, water
included in the sulfuric acid solution and/or the nitric acid
solution used for oxidation treatment, water produced by
neutralization using an anion exchange resin, water added during
dilution, and the like are included.
[0081] Next, the dispersion liquid is applied to the region where a
transparent conductive film will be formed (step S6-1).
[0082] The application of the dispersion liquid can be performed
using, for example, the screen printing method, the bar coater
printing method, the spin coating method, or the like.
[0083] It is also possible to dry the dispersion liquid to produce
a transparent conductive material (step S6-2).
[0084] When a transparent conductive material is produced by drying
the dispersion liquid, storage and transfer become easy. When the
transparent conductive material produced by drying the dispersion
liquid is added to a medium such as water, a dispersion liquid can
be easily produced.
[0085] When the transparent conductive material produced by drying
the dispersion liquid is processed into a powder form, storage and
transfer become even easier. Furthermore, it becomes even easier to
disperse the transparent conductive material in a medium such as
water.
[0086] Next, the applied dispersion liquid is dried to form a
transparent conductive film (step S7-1).
[0087] The drying of the applied dispersion liquid may be, for
example, natural drying, drying by heating, etc.
[0088] Before the applied dispersion liquid becomes completely dry,
the nanoimprint method may be used to form a transparent conductive
film having a desired configuration (step S7-2).
[0089] In this case, the formation using the nanoimprint method may
be performed immediately after the application of the dispersion
liquid, or may be performed when the applied dispersion liquid is
in a semidry state.
[0090] In the case where the transparent conductive film is formed
of ITO (indium tin oxide) or the like, the transparent conductive
film needs to be formed using the photolithography method, the dry
etching method, etc. This causes complicated formation processes
for the transparent conductive film, increased costs, etc. In
contrast, by the embodiment, a transparent conductive film having a
desired configuration can be easily obtained.
Example
[0091] Next, an example is illustrated.
[0092] First, the production of carbon nanotubes serving as the
source material in producing nanographene is illustrated.
[0093] Ethanol was supplied into a reducing atmosphere in which a
flat iron plate heated at 670.degree. C. was provided. The ethanol
had been heated at approximately 350.degree. C. beforehand. The
supplied ethanol is pyrolyzed to produce carbon nanotubes on the
flat iron plate. The carbon nanotubes produced on the flat iron
plate were mechanically scraped together to obtain carbon nanotubes
serving as the source material.
[0094] Next, the carbon nanotubes thus obtained were used to
manufacture a transparent conductive material, a dispersion liquid,
and a transparent conductive film.
[0095] First, the carbon nanotubes were put into a mixed acid
solution, and heating and stirring were performed to treat the
carbon nanotubes by oxidation.
[0096] The mixed acid solution was a solution in which sulfuric
acid and nitric acid were mixed at a ratio of 1:4. The amount of
the mixed acid solution was 100 ml.
[0097] The amount of carbon nanotubes was 1 gw.
[0098] The heating and stirring were performed on a hot plate.
[0099] The heating temperature was set to 200.degree. C., and the
stirring rotation rate was set to 300 rpm. The heating and stirring
were performed for 6 hours.
[0100] By performing the above oxidation treatment, the carbon
nanotubes were broken up to produce nanographene and polar groups
were introduced onto the surface of the nanographene.
[0101] FIG. 4 described above shows the measurement results of the
particle size distribution in the liquid before performing
oxidation treatment and the particle size distribution in the
liquid after performing oxidation treatment.
[0102] As shown in FIG. 4, when carbon nanotubes are treated by
oxidation, nanographene of less than 100 nm can be produced.
[0103] A measurement by FT-IR (Fourier transform infrared
spectroscopy) has revealed that at least an amino group, a hydroxyl
group, a mercapto group, an organic amino group, an alkoxy group, a
cyano group, a nitromethyl group, and a bis(alkoxycarbonyl)methyl
group have been introduced onto the surface of the
nanographene.
[0104] Next, the liquid after nanographene was produced by
oxidation treatment was cooled, then water was added to dilute the
liquid approximately 20 times, and an anion exchange resin was put
in to neutralize the liquid to neutrality.
[0105] After that, filtration etc. were performed to remove the
anion exchange resin; thus, a dispersion liquid was produced.
[0106] When dilution with water is performed, a temperature
increase due to the reaction heat can be suppressed and therefore
the anion exchange resin can be protected.
[0107] Furthermore, when dilution with water is performed, the
concentration of sulfuric acid and nitric acid in the liquid can be
reduced and therefore the anion exchange resin can be
protected.
[0108] Next, a solution in which poly(ethylene oxide) was dissolved
was added to the dispersion liquid.
[0109] This process was performed such that the ratio of
nanographene and poly(ethylene oxide) in the dispersion liquid to
which the solution with poly(ethylene oxide) dissolved was added
became 1:19.
[0110] Then, the dispersion liquid to which the solution with
poly(ethylene oxide) dissolved was added was applied onto a glass
substrate using the bar coater method. The workpiece was dried by
heating; thus, a transparent conductive film was produced.
[0111] FIG. 1 shows the measurement results of the visible light
transmittance of the transparent conductive film. FIG. 2B shows the
measurement results of the surface electric resistance value of the
transparent conductive film.
[0112] As shown in FIG. 1, the transparent conductive film
according to the embodiment can make the visible light
transmittance higher than the transparent conductive film including
carbon nanotubes.
[0113] As shown in FIGS. 2A and 2B, the transparent conductive film
according to the embodiment can make the surface electric
resistance value lower than the transparent conductive film
including carbon nanotubes.
[0114] The embodiments illustrated above can provide a transparent
conductive material, a dispersion liquid, and a transparent
conductive film that can improve transparency and conductivity and
methods for manufacturing the same.
[0115] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions. Moreover, above-mentioned embodiments can be combined
mutually and can be carried out.
* * * * *